There is currently a substantial interest in catalytic conversion of ethanol, including steam reforming, partial oxidation, and dehydrogenation, and even in direct ethanol fuel cells (DEFCs). We have investigated adsorption and reaction of several C₂-organic molecules, such as ethanol, acetaldehyde, and ethylene oxide, and reactive intermediates such as surface-bound ethoxy and ethyl groups on a Pt(111) single-crystal surface and two, ordered Sn/Pt(111) surface alloys: the (2x2) and (√3x√3)R30°-Sn/Pt(111) surfaces with θ_Sn = 0.25 and 0.33, respectively, as prepared by vapor deposition of Sn on a Pt(111) single-crystal substrate. The use of more than one Pt-Sn alloy enables us to probe how local surface structure and composition governs reactivity and selectivity of such alloys. Working in UHV allow us to explicitly exclude or include what is expected to be an important influence on this chemistry, i.e. the presence of surface oxygen and Sn in an oxidized state.